428
FXUS61 KCTP 090618
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
118 AM EST Fri Dec 9 2016
.SYNOPSIS...
A upper leveltrough over the Great Lakes will pivot eastward
across the region over the next couple of days. A prolonged
period of lake effect snowfall will bring significant snow
accumulations to northwest PA through Saturday. High pressure
will briefly build into Pennsylvania late Saturday, then a weak
low pressure system is likely to track west of Pennsylvania
through the Great Lakes Sunday into Monday. Unsettled weather will
persist next week with additional storm chances by both mid week
and again late next week.
&&
.NEAR TERM /UNTIL 8 AM THIS MORNING/...
The big band broke up almost completely as expected and the snows
are re-orienting to more of a general area and should go to
short-fetch bands in a couple of hours. The connections to
upstream lakes should not form until late tonight or early Fri.
Interestingly, the newest NAM actually paints a picture of an
extremely long fetch band/qpf beginning in LS, then over LM, over
Saginaw Bay (part of LH), over far srn LH (pretty close to Lake
St Clair), and finally over LE into NW PA on Fri! Wow. If it can
really manage to pull moisture from 5 of the 6 Great Lakes (yes,
Lake St Clair counts) with one band, that would be impressive.
Prev...
The main band is hanging over wrn NY and piling it onto nrn/cent
Chaut and Catt Cos. Saw BUF had a report of 17" of new snow in
Perrysburg - only HiRes WRF- ARW seems to be doing really well at
placement of the band and surrounding lighter area of SHSN coming
off LE. It along with the HRRR make a decent 20-30 degree veering
to the mean llvl wind and quickly break the main band up before
midnight - if not by 10 PM. The shorter fetch keeps the smaller
and more numerous bands within 70mi of the lake shore for a bit
until a good LH/Georgian Bay connection(s) develop later tonight.
Have tried to draw this into the POPs for the next few hours.
Otherwise all is as expected.
Prev...
Mid cloud deck associated with sheared 5h trough exiting my
southeastern counties this afternoon. Meanwhile...colder air
overspreading western and central areas has promoted stratus
development and flurries reaching into the central mountains.
Organized intense lake effect snow banding remains north of the
PA/Ny border as expected...and HRRR continues to indicate a slow
southward drift in time tonight...with moderate snowfall and
accumulations dropping south of the PA/NY border tonight..
Radar imagery shows clear trend shore-hugging snow banding
along the Lake Erie shoreline for now...thanks to lee shore
troffing induced by warmer lakes. Consensus of hi res models drops
the main band southward towards PA tonight before event evolves
into a Lake Huron connection with NW to SE oriented bands
overnight into Friday morning.
Little change to forecast storm total snow amounts as 12"+
locally expected over western portions of Warren County by
Saturday. Mins tonight will range from the lower 20s northwest
to the upper 20s southeast.
&&
.SHORT TERM /8 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Long duration lake effect snow event continues on Friday as
anomalously cold cross-lake flow maintains multiband le snow event
across the northwest Pa. Model soundings showing a deep, moist
boundary layer with an inversionheight around 700MB and although
the 850mb temps of around -11 to -14C sufficient to maintain
moderate to heavy banding from relatively warm lake waters of
around 50F.
The passage of a shortwave around midday Friday could briefly
support lake effect snow extending well downwind of the lakes,
with a quick coating likely in the ridge/valley region of Central
Pa and possibly even into parts of the Susq Valley.
The boundary layerflow is progged to remain close to 270 degrees
across Southern Pa, excluding the Laurel Highlands from a direst
link to lake moisture. However, persistent upslope flow should
yield occasional light snow with accumulations of 1-2 inches
between Friday and Sat morning.
Although not an exceptionally cold air mass for this time of the
year, this will be the coldest air mass so far this season with
temps 5-10F below normal Friday/Saturday. A gusty wind will make
it feel even colder.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Gradually improving conditions heading into Sat across the NW
Mtns as lake effect snow bands become more scattered and slowly
wind down. Still potential for a renegade snow band (with Lake
Huron connection) to stretch into the central mtns Fri night with
localized impacts though as trough lifts out. However, WSWfetch
off the lakes should continue to produce snow showers until Sat
evening across the N Mtns.
Breezy winds abate Fri night, with clearing skies across Southern
Pa late Friday night and Saturday as surface high pressure builds
in from the Ohio Valley.
High pressure will bring a brief period of tranquility Sat
evening. However, a developing overrunning scenario is expected
Sunday into Monday, as weak low pressure lifts into the Eastern
Grt Lks and high pressure remains lodged over northern New Eng.
Enough cold air is in place to support a light snowfall across
much of area by Monday AM, with GFS bringing light precip into the
area on Sunday earlier than the ECMWF. Model consensus low track
west of PA should bring in enough warm air to cause snow to
change to rain across Southern PA, and esp the Lower Susq Valley,
a before precip tapers off later Monday.
A bit cooler than normal temps indicated early next week, but
longer range models indicate a significant cold front passage
Wed with noticeably below normal temps filtering in for the rest
of next week.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Cold W-NW flow pattern downwind of the Great Lakes will continue
to support a prolonged period of MVFR/IFR conditions over the
western 1/3 of the airspace into the weekend, with frequent lake
effect/upslope snow showers at KBFD/JST. MVFR cigs and ocnl visby
reductions in -shsn are possible over the central terminals with
VFR prevailing across the eastern sites. Expect sfc wind gusts
20-25+kt from 270-300 degrees for most of today before winds
subside after 10/00z. Lake effect snow showers should decrease in
coverage and intensity by later Saturday as area of high pressure
briefly slides over the airspace. Low pressure tracking from the
lee of the Rockies to the Ohio Valley will bring a broad area of
snow/rain to the area Sunday into early Monday.
Outlook...
Sat...MVFR/IFR western 1/3 with snow showers decreasing.
Sun-Mon...Widespread MVFR/IFR in snow/rain. Becoming breezy Monday
night with snow showers over the wrn 1/3.
Tue...VFR to MVFR cigs. Snow showers ending.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
Lake Effect Snow Advisory until noon EST Saturday for PAZ005.
Lake Effect SnowWarning until noon EST Saturday for PAZ004.
&&
$$
SYNOPSIS...DeVoir
NEAR TERM...Dangelo/DeVoir
SHORT TERM...DeVoir
LONG TERM...Fitzgerald/RXR
AVIATION...Steinbugl